x/tools/present: add command line flag to enable presenter notes

Change-Id: I9d4414ce8bafcb13f53361b45774f379bacd886b
Reviewed-on: https://go-review.googlesource.com/21486
Reviewed-by: Andrew Gerrand <adg@golang.org>

cmd/present/local.go

@@ -31,6 +31,7 @@ var (
 
 func main() {
 	flag.BoolVar(&present.PlayEnabled, "play", true, "enable playground (permit execution of arbitrary user code)")
+	flag.BoolVar(&present.NotesEnabled, "notes", false, "enable presenter notes (press 'N' from the browser to display them)")
 	flag.Parse()
 
 	if *basePath == "" {
@@ -85,6 +86,9 @@ func main() {
 	}
 
 	log.Printf("Open your web browser and visit %s", origin.String())
+	if present.NotesEnabled {
+		log.Println("Notes are enabled, press 'N' from the browser to display them.")
+	}
 	log.Fatal(http.Serve(ln, nil))
 }
 

present/code.go

@@ -15,7 +15,8 @@ import (
 	"strings"
 )
 
-// Is the playground available?
+// PlayEnabled specifies whether runnable playground snippets should be
+// displayed in the present user interface.
 var PlayEnabled = false
 
 // TODO(adg): replace the PlayEnabled flag with something less spaghetti-like.
@@ -23,6 +24,10 @@ var PlayEnabled = false
 // value that contains various global metadata required when rendering
 // templates.
 
+// NotesEnabled specifies whether presenter notes should be displayed in the
+// present user interface.
+var NotesEnabled = false
+
 func init() {
 	Register("code", parseCode)
 	Register("play", parseCode)

present/parse.go

@@ -35,9 +35,10 @@ func Template() *template.Template {
 func (d *Doc) Render(w io.Writer, t *template.Template) error {
 	data := struct {
 		*Doc
-		Template    *template.Template
-		PlayEnabled bool
-	}{d, t, PlayEnabled}
+		Template     *template.Template
+		PlayEnabled  bool
+		NotesEnabled bool
+	}{d, t, PlayEnabled, NotesEnabled}
 	return t.ExecuteTemplate(w, "root", data)
 }